The present invention relates to a Heating, Ventilation, Air Conditioning (HVAC) fan controller device and in particular to a circuit providing an extended fan run time when such extended time improves overall efficiency.
Residential and commercial HVAC system power consumption in the United States accounts for 30% of average summer peak-day electricity loads, 14% of total electricity use, and 44% of total natural gas use, as reported by the US Energy Information Agency Residential and Commercial Energy Consumption Surveys from 2003 and 2009.
Known gas furnace central heating systems are controlled by thermostats which energize a relay to turn on the gas furnace heat source with a brief delay followed by turning on the heater ventilation fan at a lower fan speed than the higher fan speed used for cooling. Unfortunately, maintaining a lower heater ventilation fan speed often results in increased heat soak within the central heating unit and the portion of the heat generated by the heat source not delivered to conditioned space is lost to the environment. The heat loss increases the central heating unit operational time consuming more energy. Further, the amount of heat soak increases as the central heating unit is operated for longer periods of time leaving significantly more unrecovered energy and higher temperatures (i.e., 260 to 350 degrees Fahrenheit) in the heat exchanger after the heater ventilation fan is turned off. In most heating systems a significant portion of this unrecovered heating energy is wasted and lost to the environment after the heat source and the heater ventilation fan are tuned off.
Known direct-expansion cooling systems are controlled by thermostats which turn on a cooling ventilation fan when the cool source is energized and turn off the fan when the cool source is de-energized. When the cooling source is de-energized there is a significant amount of cold refrigerant left in the evaporator which is not used to deliver sensible cooling capacity to the conditioned space and this sensible cooling capacity is lost to the environment after the cool source and the cooling ventilation fan are tuned off. This increases the cooling system operational time and energy use.
Known heat pump, electric resistance, and hydronic heating systems are controlled by thermostats which turn on the ventilation fan when the hydronic heat source is energized and turn off the fan when the heat source is de-energized. Hydronic heating and cooling systems circulate a liquid from a central location to a heat exchanger in a forced air unit (FAU). Known heat pump and hydronic systems do not provide a fan-on delay. Nor do heat pump and hydronic systems provide a heating fan-off time delay due to lower heat exchanger temperatures of 130 to 180 degrees Fahrenheit which are 2 to 3 times lower than gas furnace heat exchanger temperatures. During the start-up period there is no useful heating delivered by the ventilation air which can waste fan energy and cause thermal comfort issues for building occupants. When the heat source is de-energized there is a significant amount of heating energy left in the heating coil which is not used to deliver heating capacity to the conditioned space and this heating capacity is lost to the environment after the heat source and the heating ventilation fan are tuned off. This increases the heat pump, electric resistance, or hydronic heating system operational time and energy use.
U.S. Pat. No. 6,684,944 (Brynes et al, 2004) and U.S. Pat. No. 6,695,046 (Brynes et al, 2004) disclose a variable speed fan motor control for forced air heating/cooling systems using an induction-type fan motor controlled by a controller circuit which is operable to continuously vary the speed of the fan motor during a start-up phase and a shut-down phase of the heating and/or cooling cycle. The controller circuit includes temperature sensors which are operable to control start-up and shutdown of the fan motor over continuously variable speed operating cycles in response to sensed temperature of the air being circulated by the fan. Brynes teaches control of the heater fan from low to high speed but the high speed is limited specifically to the motor speed used for heating which is low, medium, or medium high and not the motor's high speed used for cooling. Byrnes' patents do not include a method or a fan relay to energize the high speed used for cooling after a short time period when the heat exchanger has reached its maximum temperature to deliver more heating output to satisfy the thermostat temperature sooner and save heat source energy. Brynes' does not teach a variable fan-off time delay based on AC compressor or heat source operational time.
U.S. Pat. No. 4,369,916 (Abbey 1983) discloses a 120 VAC heating or cooling system fan override relay control to immediately start the blower to circulate air when the heating or cooling element turns on and continue to operate the override for a fixed timed interval by a time delay relay after the heating or cooling element turns off. U.S. Pat. No. 4,369,916 teaches starting the blower fan instantly when the heating element is turned on and not waiting for the heat exchanger to reach maximum temperature before turning the fan from the low speed used for heating to the high speed used for cooling. U.S. Pat. No. 4,369,916 does not vary the fan-off time delay based on air conditioning compressor or heat source operational time.
U.S. Pat. No. 6,464,000 (Kloster 2002) discloses is a temperature controlled device for a two-stage furnace: 1) low fan speed for low heat mode, and 2) higher fan speed for high heat mode. The higher fan speed is limited to available heater fan speeds; not the high speed used for cooling. U.S. Pat. No. 6,464,000 does not provide instructions for a variable fan-off time delay based on heat source operational time and does not provide instructions to initially operate the heater fan at the low speed used for heating and switch to the high speed used for cooling after the heat exchanger has reached maximum temperature.
U.S. Pat. No. 5,248,083 (Adams 1993) discloses an adaptive furnace controller using analog temperature sensing to maintain a constant preselected heat exchanger temperature (i.e., 120 Fahrenheit) during operation and operates the fan time delay until a fixed lower heat exchanger temperature (i.e. 90 Fahrenheit) is reached. The adaptive furnace control regulates a controllable valve to adjust burner firing rate, thereby holding heat exchanger operating temperature constant to create constant on/off times based on the previous cycle on/off times of the furnace by regulating circulation blower speed. By increasing blower speeds to shorten “on” times or decreasing blower speeds to increase “on” times, and thereby achieving optimum cycle times.
ICM Controls, Inc. (www.icmcontrols.com) has manufactured on delay/off delay controls for HVAC circulating fans for more than 25 years. The ICM fan delays connect between the fan “G” terminal of a thermostat to an HVAC fan relay used to energize the HVAC fan, but the on delay/off delay are fixed time delays and only have one input and one output to interrupt and control the fan. The present invention monitors the fan “G” signal as a proxy for AC compressor operation and varies the extended fan-off time delay for cooling based on AC compressor operational time.
U.S. Pat. No. 5,142,880 (Bellis, 1992) discloses a solid state control circuit for use in connection with existing low-voltage thermostat terminals of a split-system or packaged HVAC system having a refrigerant system compressor and condenser with outdoor fan and an evaporator and gas-fired furnace or electrical heating elements with indoor blower fan. The U.S. Pat. No. 5,142,880 relates generally to systems for increasing the efficiency of air conditioning units by continuing the blower run time after the compressor is turned off. Specifically, the U.S. Pat. No. 5,142,880 claims an air conditioning control unit comprising a low voltage room thermostat fan terminal, a low voltage compressor relay terminal, a timing circuit means, a sensitive gate triac, and a power triac. The U.S. Pat. No. 5,142,880 also claims a method for controlling the on-off time of an indoor fan that is controlled by and associated with an indoor thermostat for a room air conditioning system. The apparatus of the U.S. Pat. No. 5,142,880 is not programmable or adaptable. It does not have a fixed delay from one system to another. The delay is related to the supply voltage, which varies from system to system. Bellis provides constant current to the triac gates on the order of 6 milliamps. The total current draw is even higher than that when all components are included. Many systems have do not accommodate this much current draw through control relays without causing a humming noise which irritates the user. The Bellis design momentarily de-energizes the relay when switch from thermostat driven fan to his delay. This can cause relay chatter and excessive wear. Bellis does not provide for an override function if the unit fails. The Bellis design is a “fixed” delay. Bellis does not disclose a variable fan-off time delay based on air conditioning compressor or heat source operational times or increasing the heater fan speed from the low speed used for heating to the high speed used for cooling after the heat exchanger has reached the approximate maximum temperature.
In U.S. Pat. No. 5,882,233 Noto teaches of a device used to extend the fan run time and also periodically activate the fan during times the system is not calling for heating or cooling. Noto requires the circuit to have access to the 24 VAC signals from the AC transformer. This requirement precludes his device from being connected directly to the thermostat since most thermostats do not have both the hot and neutral legs of the transformer. Household wiring only provides the hot (red) signal to the transformer. Although Noto teaches of a range of delays, his invention uses fixed times for the delays. The delays in Noto's invention are not based on the duration of the air conditioning compressor or heat source operational time.
U.S. Pat. No. 4,842,044 (Flanders et al., 1989) provides a heating and cooling control system that works by energizing a fan or other fluid circulating device to circulate fluid and effect thermal transfer of energy from the fluid to the spaces being heated and by de-energizing the circulating means at a selected time interval after de-energization of he heating and control system. The U.S. Pat. No. 4,842,044 also claims a heating control system comprising a switching means to effect energization of the fluid circulating means, a switching control means that is energizable in response to operation of the control circuit, and an additional circuit means that energizes the switching control means a selected time interval after de-energization of the heating system. The U.S. Pat. No. 4,842,044 is intended to increase the time the fan is turned on after a heating cycle to improve energy efficiency. The device draws power continuously from the gas solenoid through a 680 ohm resistor, and this method has proven to be problematic in practice. Too much current drawn in this way, can cause a humming noise in the gas valve and false operation. The U.S. Pat. No. 4,842,044 also enables the fan relay to activate the blower as soon as the gas valve is activated. This results in cool air being circulated throughout the home since the plenum is not sufficiently warm. Normal heat operation retards the blower until the temperature in the plenum reaches a preset operating temperature.
The U.S. Pat. No. 4,842,044 also requires the addition of a relay circuit. This relay must be active the entire time the fan is to be off, creating a significant current draw even when the system is in not calling for heating or cooling. The U.S. Pat. No. 4,842,044 also describes fixed delays. It has no way to adapt the fan delay times either by user input or by the compressor run time. The delays provided by the U.S. Pat. No. 4,842,044 are also subject to the variations of the components selected. Additionally, although Flanders touches on the subject of how his invention works when the fan switch on the thermostat is moved from the AUTO position to the ON position, as described, there is no way for the fan to come on when the occupant requests.
In U.S. Pat. No. 4,136,703 Kinsey teaches of a device that intervenes with the controls coming from a thermostat and going to the heating/cooling system. The U.S. Pat. No. 4,136,703 discloses a fixed upper limit to the time that the compressor or heating source can be activated and then his invention adds additional time to the blower fan. This activity can increase the efficiency of an air conditioner system by allowing a certain amount of water to condense on the evaporator coil and then re-evaporating this water to cool the home. The amount of water collected will vary based on the humidity of the ambient air. Having a fixed compressor run time with a fixed blower time can create a less efficient system than the current invention. In many environments, limiting the compressor run time and counting on evaporative cooling to reduce the home's temperature will increase the time required to cool the home. In many cases, the desired set point may never be achieved.
In U.S. Pat. No. 7,240,851, Walsh teaches about a furnace fan timer. The Walsh device is strictly a timer with a user programmable interval and duration. The device runs continuously in a never ending loop counting down minutes before operating the fan and then counting the minutes to keep the fan activated. Walsh's device is not compatible with air conditioner systems. Most thermostats connect the fan switch to the air conditioner compressor switch when operating in the automatic fan mode. In systems with air conditioners, Walsh's invention will activate the air conditioner compressor when it turns on the fan. This requires users to turn off the circuit breakers for their air conditioner systems when using his device. Walsh's invention has two interchangeable wire connections.
In U.S. Pat. No. 2,394,920, Kronmiller (assigned to Honeywell) teaches of an HVAC thermostat device to control room temperatures using a pair of thermally responsive bimetallic strips mounted within a circular-shaped housing to control space cooling or heating equipment using low voltage signals. In U.S. Pat. No. 7,140,551, de Pauw (assigned to Honeywell) teaches of a similar HVAC thermostat device with a simplified user interface and circular-shaped housing to control space cooling or heating equipment using low voltage signals. U.S. Pat. Nos. 2,394,920 and 7,140,551 provide no instructions about how to monitor the fan, AC compressor, or heat source to provide a variable fan-off time delay to recover and deliver useful cooling and heating energy otherwise wasted. The prior patents do not teach about increasing heater fan speed from the low speed used for heating to the high speed used for cooling.